Fluorine resins are fit for various uses because they have superior properties (e.g. oil and water repellency, sliding property, stain resistance, heat resistance, chemical resistance and electrical properties) in comparison with other resins. However the fluorine resins have disadvantages that it is difficult to apply adhesives, coatings and the like to the fluorine resins or to laminate the fluorine resins with other materials, said disadvantages being attributable to the inactive surface of the fluorine resins.
Various processes for modifying the surfaces of the fluorine resins have hitherto been proposed. For example, E. R. Nelson et. al. (Ind. Eng. Chem., vol. 50, 1958, pp. 329-330) describe the use of a complex solution prepared from a tetrahydrofuran solution of metallic sodium and naphthalene. In this technique, not only it causes trouble from the viewpoint of working hygiene because the complex solution is unstable and liable to cause ignition during the treatment of the fluorine resins, but also adhesive and wetting properties and the like of the modified surfaces of the fluorine resins decrease remarkably under the condition of sunlight exposure or high temperature.
Tsunoda et. al. [Kogyo Zairyo (Engineering Materials), vol. 29 (No. 2), 1981, p. 105] describe the use of a glow discharge. In this technique, a modification effect of the surfaces of the fluorine resins is remarkably inferior to that of nonfluorine resins such as polyethylene and the like.
Japanese Patent Publication (KOKOKU) No. 22108/1978 describes the use of a high frequency sputter etching under low pressure. In this method, there are several disadvantages that (i) a treating speed is slow, (ii) resinous residues formed during the sputter etching are deposited to inner parts of an expensive, large-sized treating apparatus with a vacuum system, and (iii) an abrasionable, irregular surfaces of the fluorine resins do not bring about sufficient adhesive properties and application properties of coatings for low fluidable adhesives, coatings and the like.
Japanese Patent Publication(KOKAI) No. 196834/1990 describes the use of laser beam in a special gaseous atmosphere such as B(CH.sub.3).sub.3 and AI(CH.sub.3).sub.3. According to this method, a treating speed is slow, and a strong poisonous gas and an expensive, large-sized treating apparatus are inevitably required.
Japanese Patent Publication (KOKOKU) No. 57143/1991 describes the use of excimer laser beam, said laser beam being directly irradiated to the fluorine resins. According to this technique, adhesive and wetting properties of the surfaces of the fluorine resins cannot sufficiently be improved.
Japanese Patent Publications No. 21928/1983 (KOKOKU), No. 127442/1990 (KOKAI) and No. 58375/1991 (KOKOKU) describe the use of plasma sputter etching at low temperature. In this method, it is difficult to obtain high adhesive strength because of the chemical composition of the treated surfaces of the fluorine resins. In order to achieve the same higher adhesive strength as that obtained according to the method by Nelson et al., the surfaces of the fluorine resins must be treated for long-time under the narrow treating condition. Therefore said method is insufficient as an industrial treating technique.
Japanese Patent Publication (KOKAI) No. 125208/1993 discloses the method wherein ultraviolet laser beam is irradiated on the fluorine resins with which light-absorbing materials are kneaded previously. However this method cannot be applied to a surface modification of ready-made molded articles made of fluorine resins because the laser beam must be irradiated after a light-absorbing material is kneaded in the fluorine resins.